1. Field
One embodiment of the present invention relates to an optical disk device and power supply method that utilize a single power source voltage to generate different output voltages for driving types of semiconductor laser diodes.
2. Description of the Related Art
Recently, the integration density of digital ICs has been markedly enhanced. Along with this, an attempt is made to reduce the cost by integrating control hardware of an optical disk device as a digital IC and using software for digital control of a laser light source.
A typical optical disk device has types of semiconductor laser diodes for use in recording and reproduction operations of a CD, DVD and high-density DVD. The digital IC is a control processor provided for operation settings of an automatic power control (APC) circuit that controls laser outputs (laser powers) of the semiconductor laser diodes.
The semiconductor laser diodes require voltages different from each other. Conventionally, the power supply circuit in the optical disk device utilizes a single power source voltage to generate the voltages (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2003-78203). In a general example, a blue laser diode for high-density DVDs is driven by means of voltages of 6.5 and 8V, and a red laser diode for DVDs and an infrared laser diode for CDs are driven by means of voltages of 5 and 5.2V. Regarding the control processor, voltages of 1.2, 1.5, 2.5 and 3.3V are required for operation. The voltages of 1.2, 1.5, 2.5 and 3.3V are produced by stepping down the power source voltage of 5V and the voltages of 5.2, 6.5 and 8V are produced by stepping up the power source voltage of 5V.
Since the types of semiconductor laser diodes are selectively used in the recording and reproduction operations for an optical disk, the power supply circuit needs to output voltages switched between the voltages of 5 and 5.2V and the voltages of 6.5 and 8V. For example, an inrush current will not occur upon change in the output voltage between 5 and 5.2V. However, an inrush current will occur upon change in the output voltage between 5.2, 6.5 and 8V. If the inrush current occurs, it becomes difficult to stably operate the control processor and drive the semiconductor laser diode. As a countermeasure against the inrush current, the voltage switching may be eliminated by providing a plurality of independent power supply circuits, but this countermeasure resultantly increases the number of parts and the mounting area.